Speaker
Description
In digital triple-to-double coincidence ratio (TDCR) measurement systems, optical integrity and gain stability of photomultiplier tubes (PMTs) are essential to ensure reliable efficiency modelling and reproducibility of the T/D ratio. A modular portable digital TDCR system incorporating an integrated mechanical shutter and pneumatically actuated sealing mechanism was developed to enable mobile operation beyond fixed shielded installations. The design aims to maintain optical isolation during source handling while preserving measurement stability under varying environmental conditions.
The system employs a Hamamatsu R7724 PMT operated at 1800 V coupled to a CAEN DT5730SB digital pulse processing module. Performance was evaluated under four environmental configurations: (1) inside a lead-shielded cabinet with laboratory lighting on, (2) inside the cabinet with lighting off, (3) outside the cabinet with lighting on, and (4) outside the cabinet with lighting off. Total count rates and single-photoelectron (SPE) spectral centroids were analyzed to assess environmental robustness.
The maximum relative difference in total count between shielded and unshielded conditions was 4.3%, while the SPE centroid shift remained below 0.15 channel (≈0.23%). SPE peak positions and spectral shapes were consistent across all configurations, with no evidence of peak broadening or nonlinear gain variation. The observed variations are attributed to environmental background statistical fluctuations rather than light-induced gain drift.
Comparable results obtained outside the shielding cabinet under normal laboratory illumination demonstrate that the integrated shutter design effectively suppresses ambient light interference while maintaining PMT gain stability. These results support the implementation of a modular portable digital TDCR system suitable for mobile operation without significant degradation of measurement performance.